The principal objective of this proposal is to elucidate the structural and functional roles of intrinsic metal in the DNA-dependent RNA polymerases which have been shown to be Zn-metalloenzymes. We propose to achieve this objective by both biochemical and physical approaches, in particular, absorption, fluorescence, NMR, and EPR spectroscopes. RNA polymerases from both prokaryotic and eukaryotic sources, such as E. coli, bacteriophage T3, and yeast, will be studied. Specific aims to be accomplished include: (1) demonstration of the essential role of the intrinsic metal in enzyme catalysis, (2) preparation of apo-enzymes and paramagnetic metal-substituted enzymes by in vitro and in vivo approaches, (3) comparison of their biochemical and physical properties with those of native enzymes, (4) determination of the proximity relationships between the metal and other active sites on the enzymes, and (5) syncatalytic mapping of the enzymes using the metal as a probe. The universal presence of zinc in nucleotidyl transferases and the disturbance in the cell cycle of zinc-deficient cells have been established. Thus, not only will this study reveal the molecular mechanism by which the intrinsic zinc in RNA polymerase is involved in gene expression, but also it will shed some light on understanding the role of zinc in cell growth, division and differentiation.